The present invention relates to isolated polypeptides that are derived from wildtype Bacillus subtilis S-Adenosylmethionine (SAM) synthase or from a biologically active fragment thereof, wherein said isolated polypeptides comprise an amino acid sequence that, in relation to the amino acid sequence of said wildtype Bacillus subtilis SAM synthase or of the biologically active fragment thereof, comprises at least one amino acid substitution, selected from the group consisting of amino acid substitutions at positions I317 and I105. The present invention further relates to respective isolated nucleic acids, vectors, host cells, uses and methods for the production of SAM derivatives.
Almost all enzyme-catalyzed methyl transfer reactions depend on the cofactor S-adenosylmethionine (SAM). Thus, availability of this compound is crucial for application of the corresponding methyltransferases in biotechnology, e.g. in the production of valuable fine chemicals and pharmaceuticals. In cellular metabolism, this universal methyl donor is formed by adenosylation of L-methionine by SAM synthases (SAMS). However, enzymatic synthesis of SAM is not feasible for industrial application due to inhibition of most SAMS by their product SAM which results in stagnating conversion, low yield or—in life whole-cell biocatalysts—in insufficient availability of the cofactor. In addition, most SAMS enzymes does not tolerate changes in the structure of their amino acid substrate. Thus, these enzymes lack the ability to synthesize cofactor analogues from artificial methionine derivatives. From the large number of SAMS enzymes which have been characterized, only two proteins tolerably convert S-ethyl-L-homocysteine (ethionine) to S-adenosylethionine. However, these proteins are not feasible for the synthesis of SAM derivatives which enable transfer of non-natural long-chain or functionalized alkyl groups.